unit Unit1;interfaceuses  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,  Dialogs, StdCtrls;type  TForm1 = class(TForm)    Button1: TButton;    Button2: TButton;    Button3: TButton;    Button4: TButton;    procedure Button1Click(Sender: TObject);    procedure Button2Click(Sender: TObject);    procedure Button3Click(Sender: TObject);    procedure Button4Click(Sender: TObject);    procedure FormCreate(Sender: TObject);    procedure FormDestroy(Sender: TObject);  end;var  Form1: TForm1;implementation{$R *.dfm}var  List: TStringList;procedure TForm1.FormCreate(Sender: TObject);begin  List := TStringList.Create;  List.Add('aaa');  List.Add('bbb');  List.Add('ccc');  List.Add('ddd');end;// for 循环的一般用法procedure TForm1.Button1Click(Sender: TObject);var  i: Integer;  s: string;begin  for i := 0 to List.Count - 1 do  begin    s := List[i];    ShowMessage(s);  end;end;//还有这样用的procedure TForm1.Button2Click(Sender: TObject);var  i: Integer;  s: string;begin  for i := 0 to Pred(List.Count) do  begin    s := List[i];    ShowMessage(s);  end;end;//还是 for in 最方便procedure TForm1.Button3Click(Sender: TObject);var  s: string;begin  for s in List do  begin    ShowMessage(s);  end;end;//反向procedure TForm1.Button4Click(Sender: TObject);var  i: Integer;  s: string;begin  for i := List.Count - 1 downto 0 do  begin    s := List[i];    ShowMessage(s);  end;end;procedure TForm1.FormDestroy(Sender: TObject);begin  List.Free;end;end.